Researchers analyzed cow droppings and found that common prey for cows and goats included caterpillars of various butterflies, aphids, beetles, herbivorous mites, and small spiders. Some insects can avoid being eaten by the predatory cow.
Vegetarians on four legs? Not quite: a new study found that large plant-eating mammals, such as cows and goats, prey on a complex food chain of insects and other arthropods while they feed on plants.
“The prevalence of this phenomenon is so high that herbivorous mammals might also be considered insect predators. Damage to insect populations can later affect other animals that feed on insects, such as reptiles and birds,” said the researchers.
Large herbivorous mammals, such as cows, goats, sheep, deer, and zebras, consume large amounts of plant material.
Their ecological importance and impact on pastures and natural areas are considerable, and their decline or overpopulation can destabilize the system.
Many studies have examined the effects of herbivores on plant diversity and characteristics, but very few have investigated their impact on insects and arthropods living on or feeding on plants.
“In fact, insect consumption by herbivorous mammals has rarely been documented in literature, and the extent of the phenomenon and its effects on natural insect populations are unclear, as it is very difficult to observe,” said the researchers.
In the current study, published in the journal Ecology, the researchers succeeded for the first time in identifying insect DNA from the droppings of grazing cattle.
The findings revealed that cows consume a wide variety of insects while grazing, preying on a complex food chain: herbivorous insects, predatory insects, parasitic insects, and predatory spiders.
Among the common prey were caterpillars of various butterflies, aphids, beetles, herbivorous mites, and small spiders, such as jumping spiders and sheet weavers, which lie in wait on plants.
In total, insect DNA was found in 76% of the collected cow droppings, indicating the high prevalence of the phenomenon.
The researchers also identified aquatic insects and crustaceans ingested by cows while drinking.
The researchers were also able to identify which insects were more vulnerable to predation: insects, spiders, and mites limited in mobility or developing inside plant parts were more likely to be eaten.
In contrast, flying insects or those able to jump quickly were not eaten at all.
“Even more interesting was that cows avoided poisonous or aggressive insects, such as certain butterfly larvae, ants, or large spiders.
This shows that herbivores know how to avoid certain insects.
Additionally, previous research found that some insects can detect the heat and humidity from mammal breath and escape from plants in time before being eaten.
These behaviors support the perception that herbivorous mammals are insect predators,” said the researchers.
According to the researchers, the predation of complex food chains of insects and arthropods can have downstream effects on the ecosystem.
Damage to insect populations by grazing mammals can later affect insect predators, such as reptiles and birds.
Conversely, regulating the population of large herbivores, whether by natural predators or humans, can benefit vulnerable insect populations, especially in cases of overgrazing.
The next stage of research will focus on understanding the complexity and importance of this phenomenon in natural herbivore systems in African savannas.
“Arthropods in general, and insects in particular, are a central and important component of habitats, and their diversity indicates ecosystem stability,” the researchers concluded.